Heretofore, in the production of alcohol by fermentation using cellulose as a carbon source, the enzyme or acid hydrolyzate of cellulose has been used and a yeast belonging to the genus Saccharomyces has been mainly used as a seed strain. In such process, pentose (mainly xylose) derived from hemicellulose which is contained in cellulose at the rate of 10-30% is not utilized and the yield of alcohol is rather low. Therefore, cellulose is separated to .alpha.-cellulose and hemicellulose; glucose obtained from .alpha.-cellulose is utilized for the production of alcohol using a yeast of Saccharomyces and pentose obtained from hemicellulose is utilized for the production of yeast protein using a yeast capable of assimilating it as a carbon source.
Further, it has been tried to utilize the substance obtained by saccharification of cellulose with cellulase. However, cellobiose obtained by the saccharification cannot be converted to alcohol by yeasts of Saccharomyces.
As a result of studies for utilizing xylose and cellobiose which are unutilized resources, the present inventors have found a yeast capable of assimilating xylose and cellobiose as well as glucose to produce alcohol and have completed the invention.